On Tue, May 25, 2010 at 11:27 AM, Edward Ned Harvey <solar...@nedharvey.com>wrote:
> > From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > > boun...@opensolaris.org] On Behalf Of Nicolas Williams > > > > > I recently got a new SSD (ocz vertex LE 50gb) > > > > > > It seems to work really well as a ZIL performance wise. > > > I know it doesn't have a supercap so lets' say dataloss > > > occurs....is it just dataloss or is it pool loss? > > > > Just dataloss. > > WRONG! > > The correct answer depends on your version of solaris/opensolaris. More > specifically, it depends on the zpool version. The latest fully updated > sol10 and the latest opensolaris release (2009.06) only go up to zpool 14 > or > 15. But in zpool 19 is when a ZIL loss doesn't permanently offline the > whole pool. I know this is available in the developer builds. > > The best answer to this, I think, is in the ZFS Best Practices Guide: > (uggh, it's down right now, so I can't paste the link) > > If you have zpool <19, and you lose an unmirrored ZIL, then you lose your > pool. Also, as a configurable option apparently, I know on my systems, it > also meant I needed to power cycle. > > If you have zpool >=19, and you lose an unmirrored ZIL, then performance > will be degraded, but everything continues to work as normal. > > Apparently the most common mode of failure for SSD's is also failure to > read. To make it worse, a ZIL is only read after system crash, which means > the possibility of having a failed SSD undetected must be taken into > consideration. If you do discover a failed ZIL after crash, with zpool <19 > your pool is lost. But with zpool >=19 only the unplayed writes are lost. > With zpool >=19, your pool will be intact, but you would lose up to 30sec > of > writes that occurred just before the crash. > > > I didn't ask about losing my zil. I asked about power loss taking out my pool.
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